Bore hole transmission in well logging systems



June 22, 1965 G. c. SUMMERS 3,191,145

BORE HOLE TRANSMISSION IN WELL LOGGING SYSTEMS Filed May 15, 1952 3Sheets-Sheet 1 EEHA LD 7, SUMMERS IN VEN TOR.

June 22, 1965 G. C. SUMMERS BORE HOLE TRANSMI SSION IN WELL LOGGINGSYSTEMS Filed May 15, 1952 3 Sheets-Sheet 2 GERALD E. 5' UMMEHEIINVENTOR.

BYAQLVL-W AGENT June 22, 1965 c, SUMMERS 3,191,145

BORE HOLE TRANSMISSION IN WELL LOGGING SYSTEMS Filed May 15, 1952 3Sheets-Sheet 3 PEAK READ/N6 V I MM E'EHA LD 5', SUMMERS IN V EN TOR.

United States Patent 3,191,145 BORE HULE TRANSMISSION IN WELL LOGGINGSYSTEMS Gerald C. Summers, Dallas, Tex, assignor, by mesne assignments,to Socony Mobil Oil Company, Inc, a

corporation of New York Filed May 15, 1952, Ser. No. 237,853 Claims.(Cl. 340-48) This invention relates to well logging and moreparticularly to the production and transmission of more than one set ofbore hole data without objectionable crossfeed effects The invention hasbeen found to be particularly applicable to acoustic well logging andfor the purpose of illustration reference will be made to such systems.

For example, knowledge of acoustic velocity of formations is importantfrom the standpoint of both exploration for and production frompetroleum reservoirs. In applicants co-pending application for VelocityWell Logging, S.N. 192,750, filed October 28, 1950, now Patent No.2,704,364, which issued March 15, 1955, there is disclosed a system inwhich an output voltage is produced dependent upon the travel time of anacoustic pulse between a transmitter and a receiver spaced apredetermined distance apart and movable one with the other in theirpredetermined spaced relation throughout the length of a bore hole. Inaccordance with the aforesaid application there is produced a single logor curve of velocity versus depth. In accordance with the presentinvention a plurality of traces are produced, or in the alternative asingle trace is produced utilizing two independent sets of velocity datagiving more detailed and reliable information relating to the formationsalong the bore hole. In the interest of accuracy in velocitymeasurements, sharp discrete energy pulses are used. Transmission ofsuch pulses over the length of extremely long cables used to extend tothe bottom of deep bore holes presents a problem of isolation orseparation of the signals. Where arrival times of pulses at the surfaceand the timing and detection thereof are critical, crossfeeddifficulties as between adjacent cable channels may render entirelyinoperative systems attempting to utilize separate channels.

A similar problem exists in systems responsive to variations in theattenuation properties of formations. In copending application forSelective Pulse Acoustic Well Logging, S.N. 197,074, filed November 22,1950, now Patent No. 2,691,422, which issued Oct. 12, 1954, a system isdisclosed for producing a single output voltage proportional to theenergy transmitted between two points over a selected formation path. Inaccordance with the present invention, two output voltages may beproduced and utilized for more accurately defining the attenuationproperties of the formation.

In accordance with the present invention pulses spaced in time aretransmitted over the same channel for avoidance of signal crossfeed withsuitable coding means for proper separation of the time-spaced signalsat the earths surface. Thus the difiiculties generally encountered arecompletely eliminated permitting the utilization of two independent setsof data transmitted over a single channel. While, in general, multipletransmission is not new, limitations on bore hole instrumentation andthe desirability of simplicity in downhole components present problemsnot ordinarily present in multiplexing problems.

By the present invention there is provided a bore hole sensing systemwhich comprises means for periodically generating. atransient conditionin formations adjacent to the bore hole with detectors separated onefrom another at points spaced from the generating means. A signalchannel extending along the bore hole is alternately connected first toone and then to the other of the detectors in response to generation ofeach cycle of the transient condition for transmission of time separatedsignals dependent upon the condition detected at two points in the borehole. A time marker is transmitted through the bore hole having apredetermined time relation to the generation of each cycle of thecondition with means for distinctively characterizing the timing markerwhen the first of the detectors is connected to the signal channeldifferent from the marker when the second of the detectors is connectedto the signal channel.

In a further aspect of the invention two sensing units at the earths'surface are coupled to the transmission channel for reception of thetime separated signals and are controlled by means responsive to thetiming marker for coupling first one and then the other of the sensingmeans on alternate cycles of the condition to the signal channel forproducing two outputs respectively representative of the condition attwo points in the well bore. Means responsive to the outputs of thesensing means may be utilized to produce one or more distinctive logs.

Further, applicant produces a first log depending upon the travel timeof an acoustic pulse over a relatively long path or a log of one of theaforementioned outputs; and also produces a second log, the differencebetween the aforementioned outputs, to present a more detailed velocitypicture of the formations.

For further objects of the present invention and for a more completeunderstanding thereof reference may now be had to the followingdescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a schematic circuit diagram of one form of the presentinvention;

FIG. 2 is a modification of the invention;

FIG. 3 is a modified form of the multivibrator circuit for utilizingdistinctive time markers; and

FIG. 4 illustrates a modification of the invention.

Referring now to FIG. 1, an acoustic velocity well logging system isillustrated in which an acoustic pulse transducer means, including acrystal element 10, is located at depth in a bore hole 11. In theinterest of clarity, the housing and supporting means for the elementsoperating in bore hole 11 have been omitted though the circuit has beenillustrated in detail at points representative of their operativepositions in the bore hole. The crystal 10 is excited by way of anelectrical pulse produced upon discharge of a condenser 12} Condenser 12is connected in series with a relay coil 13, a primary winding 14 of apulse transformer and the cathode-anode impedance of a gas dischargetube 15 which, with crystal 10, comprise a pulse producing transducermeans. Condenser 12 may be charged from a direct current source 17positioned at the surface of the earth and having its negative terminalconnected to ground. The positive terminal is connected by Way ofresistance 18, cable conductor 19 and resistance 20 to condenser 12 andto the anode of tube 15. Tube 15 of the tetrode type has its gridsconnected to points of positive potential on the voltage dividingresistors 21 and 22.

The voltage on the condenser 12 builds up gradually as current flowsthrough resistors 18 and 20 until the voltage across it is suflicient tofire tube 15. Condenser 12 abruptly discharges through tube 15 producinga pulse in the primary 14 of the pulse transformer. The secondary 23 ofthe pulse transformer is connected directly to the terminals of thecrystal 10L The crystal 10, suitably supported in the bore hole,produces pressure variations in the adjacent formations.

The resultant acoustic pulse from the free running transducer means isdetected at two points spaced one from another and from the crystal 10.More particularly detectors 26 and 27, supported in fixed relation tocrystal 10, are positioned in the bore hole and are connected toterminals 28 and 29 of an output circuit selector which, in the formillustrated, is a relay mechanism actuated by energization of coil 13.The armature 30 of the relay is connected by way of coductor 31 to abore hole amplifier 32 whose output in turn is connected to the signalchannel 33 extending from within the bore hole to the earths surface.

Relay operation is such that armature 30 is restrained (by means notshown) in contact with terminal 28 until energization of coil 13.Thereupon armature 30 is moved into contact with terminal 29 and isthere restrained until a subsequent energization of coil 13. Steppingswitches operating in this manner are commercially available.

The relay first connects detector 26 to amplifier 32 for a first cycleof the pulse generated by crystal and then on the next cycle connectsdetector 27 to amplifier 32. On the following cycle detector 26 is againconnected to the amplifier 32. Thus the signal channel 33 carriessignals on successive cycles that are dependent upon the acoustic pulseas detected at two different points. The relay coil 13, energized uponeach discharge of condenser 12, provides a simple but reliable means forseparating the effects produced by the two detectors since the switchingtakes place before arrival of the acoustic pulse at either of thedetectors.

In order to utilize the alternate signals appearing on the signalchannel 33 there is provided at the earths surface a pair of sensingsystems 35 and 36. The sensing systems 35 and 36 are substantiallyidentical in construction and for that reason only one has been shown indetail. Where differences are necessary for utilization of the timeseparated signals appearing on channel 33 such differences have beenshown.

Consider first the sensing system 35. The construction and operation ofthis sensing system have been described in detail in the aforementionedoo-pending application S.N. 192,750. Briefly, however, the signalsappearing on channel 33 are applied by way of condenser 38 to the inputgrid of a pentode amplifier 39. The output of amplifier 39 is applied totube 40 whose output in turn actuates a blocking oscillator 41. Theblocking oscillator 41 comprises a pair of triode sections parallelconnected at both cathode and anode with the signal from tube 40 appliedto the grid of one of the sections. The anodes are connected through theprimary of a pulse transformer 42 and a reistor 43 to a source of anodepotential. A first secondary 42a of the transformer 42 is connected tothe grid of the second of the triode sections and by way ofresistor-condenser combination 44 to ground. When a voltage train havingan abrupt onset is applied to the input grid of the blocking oscillator41, a single pulse is generated in the output which produces a voltagein the RC network 44. This voltage, coupled by way of resistor 45 to theinput grid, blocks the circuit for a period depending upon the timeconstant of the network 44. As

a result, a single pulse is produced coincident with the onset of thevoltage train.

The pulse output of the blocking oscillator 41 also appears in a secondsecondary winding 49 and a third secondary winding 50. For conveniencein illustrating the circuit, the dotted lines have been placed betweenthe cores associated with windings 42a, 49 and 50 and are to be taken asindicating a common magnetic core.

The secondary windings 49 and 50 are connected in and serve to actuate anormally closed electronic switch 51. The electronic switch 51 includesa pair of triodes connected as to permit conduction bilaterally. Moreparticularly, anode 52 is connected to cathode 53 and also to aconductor 54 connected to a time varying source voltage, the nature ofwhich will hereinafter be described. Anode 55 is connected to cathode 56and also to one terminal of a condenser 57. The other terminal ofcondenser 57 is connected to ground. Condenser 57, by the momentaryenergization of the transformer secondaries 49 and 50 which opens thenormally closed switch 51, is charged to a voltage equal to the voltageappearing on conductor 54. The voltage on condenser 57 is then sensed bya cathode follower output stage 58.

The voltage across the cathode resister 59 may be utilized to actuate asuitable recorder 60 to produce a record trace which varies inproportion to the voltage across condenser 57.

The voltage on conductor 54 preferably varies monotonically and linearlyin time beginning at zero coincident with the generation of eachacoustic pulse by the crystal 1% so that the voltage across thecondenser will be maintained at all times directly proportional to thetime required for an acoustic pulse to travel from crystal 10 to one ofthe two associated detectors. When the condenser 12 discharges throughtube 15, a voltage pulse appears on the bore hole conductor 19. Thispulse is applied by way of condenser to the input grid of a monostablemultivibrator 66. The pulse output of the monstable multivibrator 66 istransmitted through condenser 67 to a voltage generator 68. The voltagegenerator 68 together with its controlling multivibrator 66 is of thetype well known in the art and is illustrated and described in detail inWave Forms, vol. 19, of the M.I.T. Radiation Laboratory Series,McGraw-Hill, 1949, at section 5.5, page 166. The operation is such thatthe voltage at point 69 is initially zero and rises monotonically andlinearly as a function of time thereafter. This voltage applied by wayof conductor 54 and through the switch 51, when opened by the pulsescoincident with transmission of a signal through amplifiers 39 and 40,charges the condenser 57. The voltage on condenser 57 is thusproportional to the time interval between generation of the pulse bycrystal 10 and the arrival at detectors 26 and 27 of the acoustic pulse.

In operation of the system of FIG. 1 the sensing means 35 is responsiveonly to pulses from detector 26 or only to pulses from detector 27.Similarly, for any one period of operation or for any one logging runthe sensing system 36 is responsive only to detector 27 or to detector26. By this means there will be produced across condenser 57 a voltagedependent upon the travel time of a pulse from crystal 10 to, forexample, detector 26. There will also be produced across condenser 57aat the output of sensing system 36 a voltage dependent upon the traveltime of an acoustic pulse from crystal 10 to detector 27.

Uncertainty as to which detector energizes which sensing system ispermitted in FIG. 1 as further explained below. More particularly, nomeans is provided to make certain that detector 26 will actuate sensingsystem 35 for every series of operations. Just which sensing system theindividual detectors actuate will depend upon the condition of thecontrol circuit at the beginning of each logging run or each series ofoperations. In this form of the invention no attempt is made to controlthe initial condition, the latter being random, but nevertheless thevoltages on condensers 57 and 57a are properly utilizable for theproduction of bore hole logs regardless of the random nature of initialchannel selection.

More particularly, the control circuit 75 is a bi-stable multivibratorand includes tubes 76 and 77. The anodes are connected through suitableload resistors to a source of anode potential (B+). The cathodes areconnected directly to ground. The control grids are conventionallycross-connected to the anodes by way of resistors 78 and 79. The gridsare also connected through bias battery 80 to ground. The timing markeron bore hole conductor 19 is applied to both grids by way of condensers81 and 82. The anode of tube 77 is connected by way of conductor 83 tothe screen grid of amplifier 39. The anode of tube 76 is connected byway of conductor 84 to the screen grid of tube 39a which is the inputamplifying pentode of the sensing unit 36.

When tube 77 is conducting, the voltage at its anode is relatively lowwith respect to ground, and thus the screen voltage on tube 39 isrelatively low so that there will be no conduction therethrough. Tube 39is thus effectively blocked when tube 77 is conducting. At the same timethe anodeof tube 76 is relatively high so that tube 39w is conductingand thus passes signals applied to its control grid from channel 33 byway of condenser 38a.

In order to illustrate operation of this system, assume tube 76 isinitially non-conducting and tube 77 initially conducting. The followingconditions or actions take place in substantially the following order:

(1) A sonic pulse is generated by crystal 10.

(2) Relay coil 13 is energized to move armature 30 to terminal 29connecting detector 27 to the amplifier 32.

(3) A timing marker appearing on conductor 19 actuates monostablemultivibrator 66 and voltage generator 68 to initiate generation of alinearly rising voltage at point 69.

(4) The timing marker is applied to the grids of both tubes 76 and 77through condensers 81 and 82, respecrtively. If it is a positive pulse,it initiates conduction in tube 76 which simultaneously stops conductionin tube 77. If a negative pulse, it is effective on the grid of tube 77to extinguish tube 77 and to initiate conduction in tube 76. As aresult, tube 39a is rendered non-conductive and tube 39 is renderedconductive.

(5) Detector 27 produces an electrical pulse in response to the receivedsound pulse which is transmitted to :the surface of channel 33 andthence through condenser 38 to the sensing unit 35.

(6) The blocking oscillator 41 momentarily opens, that is, rendersconductive, switch 51 coincident with and responsive to the electricalpulse from condenser 38 thereby to charge condenser 57 to the voltage atthat instant appearing between point 69 and ground. Switch 51 isimmediately closed, that is, rendered non-conductive, so that the chargeon and thus the voltage across condenser 57 remains constant untilswitch 51 is again opened.

(7) Condenser 12, having accumulated a charge and thus a voltagesuflicient to cause breakdown of tube 15, again discharges generating asecond sonic pulse at crystal 10.

(8) Relay coil 13 is energized to move armature 30 to terminal 28connecting detector 26 to amplifier 32.

(9) A timing marker generated coincident with discharge of condenser 12initiates another cycle of generation of a linearly varying voltage atpoint 69, the monostable multivibrator 66 and the circuit 68 havingreset themselves automatically in dependence upon their own 'timeconstants.

(10) The timing markers applied to tubes 76 and 77 extinguish tube 76and initiate conduction in tube 77, thus rendering tube 39a conductiveand tube 39 non-conconductive.

(11) Detector 26 generates an electrical voltage coincident with thearrival of the acoustic pulse which is amplified by amplifier 32 andtransmitted uphole over conductor 33. This pulse is applied throughcondenser 38a to amplifier tube 39a and thence through the sensing unit36 to charge condenser 57:; to a voltage proportional to the time oftravel of the acoustic pulse between crystal 10 and detector 26.

Thereafter the foregoing steps are repeated cyclically so that detectors26 and 27 alternately are connected to amplifier 32 and channel 33,and'sensing systems 35 and 36 are synchronously and alternately renderedconductive by the signals thus generated.

Incidentally, and as explained in detail in the above mentioned Patent2,704,364, a voltage from the monostable multivibrator 66 is connectedby way of resistorcondenser combination 90 to the suppressor grids ofboth tubes 39 and 39a. This voltage, operating in conjunction with thebattery 91 and its associated resistor and condenser circuit 92, rendersnonconductive tubes I 39 and 39a simultaneously with the transmission ofthe timing marker to prevent the timing marker itself from in the borehole.

energizing the switch 51 and the corresponding switch in the sensingunit 36. The voltage on the suppressors of tubes 39 and 39a thereaftergradually rises so that in so far as the suppressor grid is concernedboth tubes 39 and 39a may conduct shortly after appearance of the timing marker pulse.

It will now be apparent that two output voltages are produced (i.e.,across condensers 57 and 57a). They may be utilized to produce any orall of three useful velocity type logs. Recorder 60 records as a firstlog the voltage across condenser 57. The voltage across condenser 57athrough cathode follower stage is applied to a recorder 60a to produce asecond log. Additionally, the cathode of tube 95 is connected by way ofresistors 96, 9'7 and 98 to the cathode of tube 58. Any diiferences involtage across condensers 57 and 57a will thus appear, in apredetermined scaled relation which depends on the magnitudes ofresistors 96-98, across the central resistor 97. A third recorder 60b isconnected as to record as a third log the voltage across resistor 97.

Thus regardless of the initial condition of the control unit 75,recorder 60b will indicate in reliable relationship the differences inmagnitude between the voltage of condensers 57 and 57a. Since onedetector in general is positioned closer to the source 10 than the otherdetector, the larger of two voltages as indicated by the amplitudes oftraces on recorders 60 and 60a will indicate which channel is sensingthe near detector or the far detector.

This system may be utilized to particular advantage by recording twofunctions only, a first of which is a voltage proportional to the traveltime over a long path (the path between crystal 10 and the far detector27). This will give a relatively accurate measure of the velocity. For adetailed velocity study, detector 26 may be positioned closely adjacentdetector 27, and the difference in the pulse travel times for the twodistances, as recorded by recorder 60b, will indicate velocity detailfar beyond the perception of conventional velocity logging systems.

The signals for providing such data are transmitted to the earthssurface without the possibility of crossfeed, the separation of signalsbeing provided by relatively simple selector means in the bore holerequiring no components other than the relay itself. If attempts aremade to utilize separate channels Without the signal selective networksuch as is here provided for the surface units, crossfeed will renderthe system inoperative. Transmission of such signals over 6,000 to10,000 feet of cable, with cables of the type available in the industry,often has crossfeed signals of magnitudes in the order of 33 percent ormore, depending of course upon the frequency spectrum of the signalstransmitted. Such objectionable features are thus overcome, permittinguse of conventional well logging cables.

A modified system is illustrated in FIG. 2. An alternating currentsource 100 is connected by way of conductor 101 and through transformer102, conductors 103 and 104 and transformer 105 to a rectifier 106positioned Rectifier 106 is connected through resistor 107 to theacoustic signal source or crystal 108 which in turn is connected toground. When the charge on the crystal reaches a certain magnitude,discharge tube 110 breaks down to discharge crystal 108. The dischargecurrent flowing through resistors 111 and 112 and the relay coil 109actuates the stepping switch armatures 113 and 114. Armature 114 servesalternately to connect detectors 115 and 116 to the bore hole amplifier117 in the same manner as above described in connection with FIG. 1. Onalternate discharges of crystal 103 armature 113 shunts resistor 111. Ifresistors 111 and 112 are of equal value, the timing marker applied totransformer 105 and transmitted uphole to transformer 102 willalternately be of different amplitudes, bearing a relation one toanother of one to one-half.

The control system 75, corresponding with control system '75 of FIG. 1,is responsive to such distinctive markers so that tubes '76 and 77 nolonger operate from an initial random condition but rather are keyed toand synchronized with the relay Hi9. More particularly, a battery 12% isconnected in the grid circuit of tube 77 and its level adjusted togetherwith the level of battery filler so that it will not respond to timingmarkers of one-half amplitude.

The output voltages from the control network '75 appearing at terminals121 and 122 will thus be applied to sensing systems of the type abovediscussed which will be connected to terminals 125 and 11%. Thusregardless of the tendency of tubes 76 and '77 to lock into operation atrandom, the circuit operation at least after the first pulse fromcrystal 168 is keyed to relay Hi9.

FIG. 3 illustrates an alternative arrangement. The timing markers may becharacterized by reversal in polarity on alternate cycles rather thanthe variation in amplitude discussed above. This may be accomplished byreversing the circuit connections at terminals 123 and 124 of thetransformer 105, FIG. 2, under the control of relay 109. A double throw,double pole switch operated by a relay coil would be suitable. Whenmarkers of reversing polarity are utilized, the markers are applied onlyto the grid of tube 76, FIG. 3, since the positive pulse will turn tube'76 on and the negative pulse will turn tube '76 off. In this manner,output voltages at terminals E27 and 12% are in a different manner keyedto switching operation downhole.

The foregoing description has related specifically to acoustic velocitywell logging systems. Now, there will be described a system in which theattenuation properties of the earth formations are measured. Inaccordance with the embodiment of the invention illustrated in FIG. 4,two output voltages are provided for more accurately indicating theattenuation properties than is possible with prior art systems. Whereconsistent, like parts have been given the same reference characters asin FIG. 1.

The separation between the transducer lid and the detectors 26 and 27 ismade relatively large compared to the spacing between detectors 26 and27. Condenser 12 discharging through relay coil 1'3, transformer primary14 and tube 15 produces acoustic pulses in the formations adjacent thebore hole 11 for travel to the detectors. In response to repeated cyclesof discharge of condenser 12, detectors 2-6 and 27 are connected onalternate cycles to the input of amplifier 32. Signals are transmiteduphole by way of channel 33 and are applied through condensers 38 and38a to the control grids of amplifying tubes 39 and 39a. A marker pulse,generated coincident with generation of each of the pulses by thetransducer 1% is transmitted uphole by way of conductor 19 and appliedby way of condensers 81 and 82 to the bi-stable multivibrator '75.Multivibrator 75 serves to produce gating voltages for application tothe screen grids of the amplifier tubes 3% and 39a. The output ofamplifier 39 is connected to a peak reading vacuum tube voltmeter 150.The output voltage of the vacuum tube voltmeter 159 is sensed by thecathode follower stage 151. In a similar manner the si nal fromamplifier tube 39a is applied to a similar vacuum tube voltmeter 159awhose output is sensed by a cathode follower stage 151a.

In operation assume that initially the multivibrator 75 has tube 39turned on and the tube 3% turned off. The pulse detected by detector 26will then produce in the voltmeter 15% a voltage proportional to themaximum acoustic signal amplitude of energy traveling through thevarious possible paths from the transducer to the near detectors 26. Onthe next cycle of operations, tube 3% is turned on and tube 39 is turnedoff so that the detected signal from detector 27 produces in thevoltmeter th: a voltage proportional to the maximum amplitude of anacoustic signal traveling from the transducer 10 to the far detector 27.If the distance between transducer 10 and the near detector 26 is largecompared to the distance between transducers 26 and 27, the differencein the voltages produced in the voltmetcrs 259/ and 159a will be morenearly a direct measure of the attenuation of the formations than willbe obtained using a single transducer and detector.

The voltages sensed by cathode followers 151 and 151a are recorded byrecorder 6% in the same manner as illustrated in the system of FIG. 1.Of course the individual voltages for actuation of recorders, such asrecorders 6t) and dim of FIG. 1, are available in the system of FIG. 4if recordation thereof is desired.

It will be seen that within the provisions of the present inventionperiodically recurring acoustic pulses are detected at two points in thebore hole, and the signals generated upon detection are transmitted onalternate cycles to the earths surface. Timing markers producedcoincident with the generation of the acoustic pulses are utilized atthe surface for selectively actuating the surface sensing systems toproduce a pair of output voltages which may be utilized in theproduction of useful acoustic logs.

While in FIG. 1 three recorders have been shown, it will be apparentthat all traces may be recorded in a single recording unit or that aselected pair of the three traces may be produced Further, the relaysystem illustrated for switching detector channels at the downholelocation is merely exemplary of the types of systems that are suitablefor this operation. For example, a circuit downhole similar inconstruction and operation to the multivibrator and amplifying tubes 39and 39a would be suitable for applying signals from detectors 26 and 27alternately to the uphole signal channel 33. However, the relay operatedsystem is preferred because of its simplicity and minimum powerrequirement.

While the invention has been illustrated and described by severalmodifications thereof, it will be apparent that further modificationswill now su gest themselves to those skilled in the art, and it isintended to cover such modifications as fall within the scope of theappended claims.

What is claimed is:

l. in a system for logging a bore hole in which a periodically recurringtransient condition is generated in formations adjacent said bore holeby transducer means in said bore hole and detected by detectors locatedat separate points spaced from the point of generation of said conditionthe improvement which comprises means for transmitting markers from saidtransducer means to the earths surface in predetermined time relation toeach cycle of said periodically recurring condition, a signal channelextending into said bore hole from surface terminals, means responsiveto said transducer means upon generation of each said transientcondition for alternately connecting said signal channel to each of saiddetectors, a pair of sensing means at said surface terminals, meansresponsive to said markers for coupling first one and then the other ofsaid sensing means on alternate cycles of said condition to said signalchannel, and recording means responsive to the outputs of said sensingmeans.

2. A system for sensing a condition in a bore hole which comprisestransducer means in said bore hole for periodically generating atransient condition in formations adjacent said bore hole, detectorsseparated from one another at points spaced from said generating means,a signal channel extending along said bore hole, means responsive tosaid transducer means upon generation of each cycle of said transientcondition for alternately connecting first one and then the other ofsaid detectors to said signal channel for transmission thereover of timeseparated signals dependent upon said condition at two points in saidbore hole, means for transmitting markers through said bore hole inpredetermined time relation to each cycle of generation of saidcondition and means for distinctively characterizing said markers whenthe first of said detectors is connected to said signal channeldifferent from their character when the second of said detectors is soconnected.

3. In a system for producing an acoustic log of a bore hole in whichperiodically recurring acoustic pulses are generated in formationsadjacent said bore hole by a pulse source for actuation of detectorspositioned at separate points spaced from the point of generation ofsaid pulses the improvement which comprises means for transmitting timemarkers to the earths surface in predetermined time relation to each ofsaid acoustic pulses, a signal channel extending into said bore hole,means coupled to said pulse source and responsive to generation of eachof said acoustic pulses for alternately connecting said signal channelfirst to one and then to the other of said detectors, a pair of sensingmeans, means responsive to said time markers for coupling first one andthen the other of said sensing means on alternate pulses to said signalchannel, and recording means responsive to the outputs of said sensingmeans.

4. A system for sensing a condition in a bore hole Which comprisestransducer means for periodically generating acoustic pulses informations adjacent said bore hole, detectors separated from one anotherat points spaced from the point of generation of said acoustic pulses,'a signal channel extending along said bore hole, means-responsive tosaid transducer means upon generation of each of said acoustic pulsesalternately to connect first one and then the other of said detectors tosaid signal channel for transmission thereover of timerseparated signalsdependent upon said reception of said acoustic pulses by said detectors,means for transmitting markers through said bore hole in predeterminedtime relation to generation of each of said pulses, and means fordistinctively characterizing said markers when the first of saiddetectors is connected to said signal channel different from when thesecond of said detectorsis so connected.

5. In an acoustic well logging system in which periodically recurringacoustic pulses are generated in formations adjacent a bore hole bytransducer means for actuation of detectors positioned at separatepoints spaced from the point of generation of said pulses theimprovement which comprises means for transmitting time markers to theearths surface in a predetermined time relation to each of said acousticpulses,'a signal channel extending into said bore hole means coupled tosaid transducer means and responsive to generation of each of saidacoustic pulses for alternately connecting said signal channel first toone and then to the other of said detectors, a pair of sensing means atthe surface of the earth, means responsive to said time markers forrenderingfirst one and then the other of said sensing means on alternatepulses responsive to signals on said signal channel for producing ineachof said sensing means a voltage dependent upon the time betweengeneration of an acoustic pulse and reception of said pulse by both ofsaid detectors, and means for measuring the difference in said voltagesfor detailed velocity examination of formations between said detectors,

6; In an acoustic Well logging system in which periodically recurringacoustic pulses are generated in formations adjacent a bore hole bytransducer means for actuation of detectors positioned at separatepoints spaced from thepoint of generation of said pulses the improvementwhich comprises means for transmitting time markers to the earthssurface in a predetermined time relation to eachof said acoustic pulses,a signal channel extending into said bore hole, means coupled to saidtransducer means and responsive to generation of each of said acousticpulses for alternately connecting said signal channel first to One andthen to the other of said detectors, a pair of peak voltage measuringcircuits at the surface of the earth, means responsive to said timemarkers for rendering first one and then the other of said circuits onalternate pulses responsive to the signals on said signal channel forproducing in each of said circuits a voltage dependent upon themagnitudes of the acoustic pulses received by said detectors, and meansfor measuring the difference 'between said voltages for a detailedattenuation examination of the formations between said detectors.

7. A system for eliminating crossfeed effects in transmitting andutilizing time separated signals generated in response to acousticpulses produced in formations adjacent the walls of the bore hole whichcomprises a pair of detectors positioned at separate points spaced fromthe point of generation of said pulses, a transmission channel extendingfrom within said bore hole to the surface of the earth, a relay, meansfor actuating said relay in response to generation of each of saidpulses for alternately connecting said transmission channel-first to oneand then to the other of said detectors, means for transmitting a timemarker to the surface in predetermined time relation to the generationof each of said pulses, a surface system having three input circuits,means for connecting said transmission channel to two of said inputcircuits and for applying said time marker to the third of said inputcircuits, and means in said surface system for separating signals fromsaid pair of detectors comprising means connected between said thirdinput circuit and said two input circuits for rendering first one andthen the other of said two input circuits conductive on alternateoccurrences of said time marker.

'3. In a bore hole logging system the combination which comprises anexploring unit including a transducer sup ported for movement along abore hole, an energy source for periodically'exciting said transducer toproduce acoustic pulses in bore hole media adjacent thereto, a pair ofacoustic detectors in said exploring unit separated one from the otherat points spaced from said transducer for generation of voltages inresponse to said acoustic pulses, a transmission circuit extending fromsaid unit to the earths surface, means in circuit with said energysource for connecting first one and then the other of said detectors tosaid transmission circuit for producing at the earths surface a firstset of voltages comprising pulses spaced in time with alternate pulsesdependent upon said .as a time index for identify-ing the components ofsaid first set of voltages.

9. In a system for logging a bore hole the combination which comprises atransducer, an excitation circuit for said transducer including anenergy source and a coil, a pair of acoustic detectors separated fromone another at points spaced from said transducer for generatingvoltages in response to said acoustic pulses, a transmission circuitextending from within said bore hole to the earths surface, a relayactuated by said coil for connecting at a first relay circuit first oneand then the other of said detectors to said transmission circuit fortransmission of signals from said detectors to the, ear-ths surface asdiscrete time separated signals, means for producing an electrical pulsein predetermined time relation to each of said acoustic pulses, a secondrelay circuit connected to said last named means for distinctivelycharacterizing said electrical pulses on alternate cycles of saidacoustic pulses, and means for transmitting said characterizedelectrical pulses to the earths surface to produce an electrical timeindex individually to identify said voltages.

It). In a bore system for logging a bore hole the combination whichcomprises a transducer, an excitation circuit for said transducerincluding a current source and a coil for producing a magnetic field, apair of acoustic detectors separated from one another at points spacedfrom said transducer for generating voltages in response to saidacoustic pulses, a transmission circuit extending from within said borehole to the earths surface, a relay aetuated by said magnetic field forconnecting in a first relay circui-t first one and then the other ofsaid detectors to said transmission circuit for producing at the earthssurface discrete time separated signals from said two detectors, a pairof sensing units at the earths surface both connected to saidtransmission circuit, means for producing an electrical pulse inpredetermined time relation to each of said acoustic pulses, a secondrelay circuit connected to said last named means for distinctivelycharacterizing said electrical pulses on alternate cycles of saidacoustic pulses, and a control circuit at .the surface :of the earthresponsive to said characterized pulses for connecting to saidtransmission circuit on alternate cycles of said acoustic pulses firstone and then the other of said sensing units to produce two outputvoltages decpndent upon said acoustic pulses at said spaced points.

11. A system for producing an acoustic log of a bore hole whichcomprises .a transducer movably positioned in said bore hole, an energysource coupled to said transducer for periodically exciting saidtransducer to generate acoustic pulses in formations adjacent said herehole, a pair of detectors separated from one another at points spacedfrom said transducer, 21 signal channel extending along said bore hole,means in circuit with said source and responsive to each energization ofsaid tra, sducer for alternately connecting first one and then the otherof said detectors to said signal channel for transmission to the earthssurface of time separated signals dependent upon the reception of saidacoustic pulses by said detectors at two points in said bore hole, apair of sensing systems connected to said signal channel for producing apair of output voltages, means for producing an electrical pulse inpredetermined time relation With respect to each energization of saidtransducer, means for transmitting said electrical pulse to the earthssurface, a circuit control-ling system responsive to each of saidelectrical pulses and connected to both of said sensing systems forenergizing first one and then the other of said sensing systems inresponse to successive electrical pulses thereby to limit the responseof one said sensing systems to but one of said detectors and the otherof said sensing systems to the other of said detectors to produce twooutput voltages dependent upon said acoustic pulses at two points insaid bore hole.

12. In a system for producing an acoustic log of a 'bore hole in whichperiodically recurring acoustic pulses are generated in formationsadjacent said bore hole by a pulse source for actuation of detectorspositioned at separate points spaced from the point of generation ofsaid pulses the improvement which comprises means for transmitting timemarkers to the earths surface in predetermined time relation to each ofsaid acoustic pulses, a signal channel extending into said bore hole,means coupled to said pulse source and operative coincident withgeneration of each of said acoustic pulses for alternately connectingsaid signal channel first to one and then to the other of saiddetectors, a pair of sensing means, means responsive to said timemarkers for coupling first one and then the other of said sensing meanson alternate pulses to said signal channel, and recording meansresponsive to the outputs of said sensing means.

13. An acoustic logging system comprising:

a logging tool adapted for suspension in a borehole by a'cable from theearths surface, said cable including electrical conductors,

a transmitter in said tool,

means for periodically energizing said transmitter for producing asuccession of acoustic pulses,

a near detector and a far detector in said tool supported in aspaced-apart relation one to the other and both spaced to one side ofsaid transmitter, each being responsive in succession to reception fromadjacent borehole formations of said acoustic pulses for producingelectrical signals, and

circuit-controlling means disposed between said electrical conductorsand said detectors for applying to said conductors upon energization ofsaid transmitter the resultant signals from said far detector while saidnear detector is disconnected from said conductors to prevent the aplication to said conductors of the resultant signals from said neardetector and upon the next energization of said transmitter for applyingto said conductors the resultant signals from said near detector Whilesaid far detector is disconnected from said conductors to prevent theapplication thereto of the resultant signals from said far detectoruntil after the next energizat-ion of said transmitter.

1 An acoustic logging system comprising:

a logging tool adapted for suspension in a borehole by a cable from theearths surface, said cable including electrical conductors,

a transmitter in said tool,

means for periodically energizing said transmitter for producing asuccession of acoustic pulses,

a near detector and a far detector in said tool supported inspaced-apart relation one to the other and both spaced to one side ofsaid transmitter, one of which detectors is disconnected from saidconductors, each said detector being responsive to reception fromadjacent borehole formations of said acoustic pulses for producingelectrical signals, and

circuit-controlling means disposed between said con ductors and saiddetectors for disconnecting from said conductors one of said detectorsbefore arrival at said detector of an acoustic pulse from saidtransmitter and for connecting another of said detector-s to saidconductors before arrival at said last-named detector of the acousticpulse from said transmitter.

15. An acoustic logging system comprising:

a logging tool adapted for suspension in a borehole by a cable from theearths surface, said cable including electrical conductors,

a transmitter in said tool,

means for periodic-ally energizing said transmitter for producing asuccession of acoustic pulses,

a near detector and a far detect-or in said tool supported inspaced-apant relation one to the other and both spaced to one side ofsaid transmitter, each being responsive in succession to reception fromadjacent borehole formations of said acoustic pulses for producingelectrical signals, and

circuit-controlling means disposed between said detectors and saidconductors for completing a connection from one of said detectors tosaid conductors and at the same time disconnecting the other of saiddetectors from said conductors,

said connection and disconnect-ion taking place before arrival :of theacoustic pulse at either of said detectors for disconnecting the one andconnecting the other of said detectors to said conductors.

References Cited by the Examiner UNITED STATES PATENTS 2,088,588 8/37Dudley 1-81.53 2,190,686 2/40 Slichter 181-.53 X 2,200,476 5/40 Mounce181.53 2,275,736 3/42 Cloud 181-.53

BENJAMIN A. BORCHELT, Primary Examiner.

SAMUEL FEINBERG, MILTON BUCHLER, ISAAC LIZANN, BENNETT G. MILLER, SAMUELBERN- STEIN, Examiners.

13. AN ACOUSTIC LOGGING SYSTEM COMPRISING: A LOGGING TOOL ADAPTED FORSUSPENSION IN A BOREHOLE BY A CABLE FROM THE EARTH''S SURFACE SAID CABLEINCLUDING ELECTRICAL CONDUCTORS, A TRANSMITTER IN SAID TOOL, MEANS FORPERIODICALLY ENERGIZING SAID TRANSMITTER FOR PRODUCING A SUCCESSION OFACOUSTIC PULSES, A NEAR DETECTOR AND A FAR DETECTOR IN SAID TOOLSUPPORTED IN A SPACED-APART RELATION ONE TO THE OTHER AND BOTH SPACED TOONE SIDE OF SAID TRANSMITTER, EACH BEING RESPONSIVE IN SUCCESSION TORECEPTION FROM ADJACENT BOREHOLE FORMATIONS OF SAID ACOUSTIC PULSES FORPRODUCING ELECTRICAL SIGNALS, AND CIRCUIT-CONTROLLING MEANS DISPOSEDBETWEEN SAID ELECTRICAL CONDUCTORS AND SAID DETECTORS FOR APPLYING TOSAID CONDUCTORS UPON ENERGIZATION OF SAID TRANSMITTER THE RESULTANTSIGNALS FROM SAID FAR DETECTOR WHILE SAID NEAR DETECTOR IS DISCONNECTEDFROM SAID CONDUCTORS TO PREVENT THE APPLICATION TO SAID CONDUCTORS OFTHE RESULTANT SIGNALS FROM SAID NEAR DETECTOR AND UPON THE NEXTENERGIZATION OF SAID TRANSMITTER FOR APPLYING TO SAID CONDUCTORS THERESULTANT SIGNALS FROM SAID NEAR DETECTOR WHILE SAID FAR DETECTOR ISDISCONNECTED FROM SAID CONDUCTORS TO PREVENT THE APPLICATION THERETO OFTHE RESULTANT SIGNALS FROM SAID FAR DETECTOR UNTIL AFTER THE NEXTENERGIZATION OF SAID TRANSMITTER.